Limited structural studies revealed that the group e allotypic markers (e14 and e15) are located in the Fc region of rabbit IgG, and correlates with a Thr/Ala substitution at position 309 situated within the CH2 domain. Our immediate objectives are, 1.) to determine whether the group e allotypes in hare and cottontail are also Fc and Ch2 domain markers, 2.) to compare the L chain of present day Leporidae with respect to allotypic specificities, amino acid composition and intra-chain disulfide bonds, 3.) to investigate the expression of unexpected allotypes latent allotypes) in hyperimmune rabbits. BIBLIOGRAPHIC REFERENCES: McBurnette, S.K. and Mandy, W.J. Rabbit IgG Hinge Region: Site of group d allotypic specificity. Immunochemistry 12:861 (1975).